The biggest mistake in student films is that they are usually cast so badly, with friends and people the directors know. Actually you can cover a lot of bad direction with good acting. ↗
The biggest mistake that you can make is to believe that you are working for somebody else. Job security is gone. The driving force of a career must come from the individual. Remember: Jobs are owned by the company, you own your career! ↗
One of the biggest mistakes a photographer can make is to look at the real world and cling to the vain hope that next time his film will somehow bear a closer resemblance to it. ↗